Free calculator

Intermittent Fasting Calculator

Plan your intermittent fasting schedule with this calculator. Choose from 9 protocols including 12:12, 14:10, 16:8, 18:6, 20:4, OMAD, 5:2, ADF, or set your own custom hours. See your daily schedule on a visual 24-hour clock, plan different protocols for each day of the week, and find out whether your workout falls inside or outside your eating window.

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Enter your details

Fasting Protocol

First meal time

When you want to eat your first meal

Your Fasting Schedule

Example

Example figures, not your own. Worked for 16:8 with the first meal at 12:00pm. Enter your own details and press Calculate.

Protocol

16:8

16h fasting / 8h eating

Daily Schedule

Fasting starts

8:00 pm - stop eating

Eating window opens

12:00 pm - break your fast

First Meal

12:00 pm

Meal 2

3:45 pm

Last Meal

7:30 pm

Eating window closes

8:00 pm - begin fasting

Allowed during fasting: Water, black coffee, plain tea, sparkling water. Avoid anything with calories, sweeteners, or milk.

How It Works

Intermittent fasting restricts eating to a set window each day. The 16:8 protocol means 16 hours of fasting and an 8-hour eating window - the most popular and sustainable option. The 18:6, 20:4, and OMAD (One Meal a Day, approximately 23:1) protocols progressively narrow the eating window. Weekly protocols like 5:2 and ADF alternate between fasting and normal eating days. This calculator takes your preferred first meal time and calculates your entire daily schedule, including when to stop eating and when your fasting window begins and ends. Use the weekly planner to mix protocols across different days, and the workout tab to optimise your training around your eating window.

How to use it

1Select your intermittent fasting protocol (12:12, 14:10, 16:8, 18:6, 20:4, OMAD, 5:2, ADF, or Custom)
2Enter the time you want to eat your first meal
3Optionally expand Advanced Options to set meal count, workout time, and workout duration
4Click "Calculate" to see your visual clock and daily timeline
5Switch to the Weekly tab to customise protocols for each day of the week
6Check the Workout tab (if set) to see fasted vs fed training recommendations

Quick Reference

Protocol	Fasting Window	Eating Window	Typical Meals	Difficulty
12:12	12 hours	12 hours	3 meals + snacks	Beginner
14:10	14 hours	10 hours	3 meals	Easy
16:8	16 hours	8 hours	2-3 meals	Moderate
18:6	18 hours	6 hours	2 meals	Challenging
20:4	20 hours	4 hours	1-2 meals	Advanced
OMAD (23:1)	23 hours	1 hour	1 large meal	Very Advanced
5:2 (weekly)	2 full days	5 normal days	Normal on eat days	Moderate
ADF	Every other day	Every other day	Normal on eat days	Advanced

The 16:8 protocol is the most studied and sustainable for most people. Start here before trying more restrictive protocols.

How This Is Calculated

Eating window end = first meal time + eating hours Fasting window = 24 hours - eating hours

first meal time: = when you eat your first meal of the day
eating hours: = hours in your eating window (8 for 16:8, 6 for 18:6, etc.)
fasting window: = hours you abstain from caloric intake

During the fasting window, water, black coffee, and plain tea are permitted. Any caloric intake breaks the fast.

Frequently Asked Questions

Which intermittent fasting protocol is best for weight loss?

The 16:8 protocol is the most studied and sustainable for long-term weight loss. It naturally reduces calorie intake by about 300-500 calories per day. More restrictive protocols (18:6, 20:4) may produce faster initial results but are harder to maintain.

Can I drink water during the fasting window?

Yes. Water, black coffee, and plain tea are allowed during fasting and will not break your fast. Avoid anything with calories, including milk, sugar, or flavoured drinks. Staying hydrated during fasting is important.

Is intermittent fasting safe for everyone?

IF is not recommended for pregnant or breastfeeding women, children, people with eating disorders, or those with type 1 diabetes. If you have any medical condition or take medication, consult your GP before starting. Most healthy adults can safely try 16:8.

How long before I see results with intermittent fasting?

Most people notice reduced bloating within the first week. Measurable weight loss typically begins in weeks 2-4, with 0.5-1 kg per week being typical when combined with a balanced diet. Metabolic benefits like improved insulin sensitivity can develop within 2-4 weeks.

Should I work out during my fasting window?

Fasted training can increase fat oxidation and may benefit some people for low-to-moderate intensity exercise. However, high-intensity or strength training typically performs better when fuelled. If you train fasted, stay hydrated and break your fast with a protein-rich meal (30-40g protein) as soon as your eating window opens.

Can I use different fasting protocols on different days?

Yes, and many people do. A common approach is stricter protocols (18:6 or 20:4) on rest days and more relaxed ones (14:10 or 16:8) on training days. Use the weekly planner to map out your full week.

What is the 5:2 diet and how does it compare to daily fasting?

The 5:2 protocol involves eating normally for 5 days and restricting intake to 500-600 calories on 2 non-consecutive days each week. Research shows similar weight loss results to daily protocols like 16:8, but some people find it easier because there are no daily time restrictions on most days.

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